The invention broadly relates to the coating of a continuous element or web, and especially to the electrodeposition coating of a continuous sheet of metal that travels in a generally horizontal pathway through a coating apparatus.
There are presently on the market coating apparatuses which utilize rollers for supporting a sheet of metal as it travels horizontally through a bath of liquid coating solution. It has been found that the roller immediately downstream from the liquid bath can cause distortion of the undried liquid coating which adheres to the sheet of metal. Some apparatuses eliminate the use of a downstream roller by passing the sheet of metal vertically through a bath of liquid coating directly into an overhead oven, wherein the liquid coating is baked or dried onto the sheet of metal. However, such apparatuses require overly tall buildings for housing them.
U.S. Pat. No. 3,962,060 is directed to a coating apparatus which eliminates the need for rollers to support a sheet of metal traveling in a horizontal pathway. The particular apparatus shown and described in this patent utilizes successive jets of liquid coating solution as a means for supporting the sheet of metal as it travels through a bath of liquid coating solution. These jets of liquid coating solution are impinged directly against the traveling metal sheet at angles of substantially 90.degree. relative to the plane of the metal sheet. The velocity at which these jets of liquid strike the sheet of metal must be carefully controlled. Otherwise, the coating material will foam excessively and adversely affect the coating being applied to the sheet of metal. The particular coating apparatus of this patent also uses at the entrance and exit openings through which the sheet of metal enters and exits the bath of coating solution, ordinary flap seals which have proven to be unsatisfactory over extended periods of time, since the traveling sheet of metal, especially the generally ragged overlapped ends and edges of two spliced sheets of metal, gradually destroys the seals to allow the mass escape of liquid coating solution from the apparatus, such escape having a ruinous affect upon the appearance of the coating. The invention is directed to an improved apparatus which eliminates or substantially reduces some of the aforementioned problems experienced with prior art electrodeposition coating devices for coating a continuous sheet of metal.
Briefly stated, the invention is in an electrodeposition coating apparatus having a tank with a horizontally elongated treatment chamber that is provided with a pair of longitudinally spaced end walls with horizontally aligned openings through which a continuous traveling web, such as a sheet of metal, enters and exits the chamber and bath of liquid coating solution contained therein. A pair of parallel, electrically charged electrodes are disposed longitudinally in the chamber and are positioned to sandwich the traveling web therebetween. A liquid seal is provided adjacent each of the openings through which the traveling web enters and exits the chamber. Each of the liquid seals includes a pair of parallel, elongated nozzles which are disposed normal to the direction in which the web travels. The nozzles are at least coextensive with the openings and have at least one continuous slot facing the traveling web. Means are supplied for circulating liquid coating solution, under pressure, into the nozzles and uniformly out through the slots. A deflector is provided adjacent each of the slots to direct a steady flow of liquid coating solution angularly against the traveling web at an angle substantially less than 90.degree. to the plane of the web and in the direction of the chamber and into the space between the electrodes. The turbulent flow of liquid coating solution acts to support the traveling web and eliminates the need for a downstream roller, prevent the escape of liquid coating solution from the apparatus, and maintain the proper concentration of the liquid coating solution in the critical area between the electrodes.
Other aspects of the invention are the provision of means for supplying liquid coating solution to the chamber at a level which is vertically lower than the electrodes, and for continuously circulating liquid coating material into the chamber to a level where the electrodes are submerged in the liquid coating solution. Means are also disposed adjacent opposing surfaces of the traveling web outside the chamber and beyond the liquid seals, for directing air, under pressure, angularly against the traveling web in the direction of the liquid seals and chamber to help prevent the escape of liquid coating solution, to aid in the support of the traveling web, and to minimize and control drag-out of the liquid coating material on the traveling web, i.e. the thin film of liquid coating material that adheres by surface tension to a traveling web such as a sheet of metal.